Expectations for radio communication using a millimeter wave band are recently running high. Miniaturization and cost reduction are required to use a millimeter wave band radio communication technique in consumer applications. A process using an expensive material, such as GaAs, has hitherto been applied to manufacture of a millimeter wave band RF circuit.
Incidentally, if a CMOS (Complementary Metal-Oxide Semiconductor) process can be applied to manufacture of a millimeter wave band RF (Radio Frequency) circuit, cost for manufacturing a millimeter wave band RF circuit can be curtailed. However, in a case where a circuit, such as an amplifier, is configured for a millimeter wave band, when a circuit, such as a matching circuit, is designed by means of a distributed constant circuit, an area of a passive circuit, such as a transmission line, becomes greater than an area of an active element, such as a transistor. Consequently, difficulty is encountered in miniaturizing the circuit.
A slow wave configuration has generally been known as a technique for miniaturizing a transmission line.
For instance, a proposed configuration (see; for instance, Patent Document 1) uses, as a dummy ground (Dummy Ground), strip lines that are perpendicular to a signal line and ground lines of the transmission line, and the strip lines having the same electric potential as that of the ground lines are positioned close to the signal line.
FIG. 8 is a view showing a configuration of the transmission line. Strip lines (Strip Lines) 30 perpendicular to a signal line 14 and ground lines 16a and 16b are used as a dummy ground. By means of the configuration, capacitance of the transmission line can be increased by making the dummy ground, which has the same electric potential as that of the ground lines, close to the signal line. In the configuration, the strip lines cross at right angles the signal line, whereby no electric current flows. For this reason, inductance (Inductance) L of the transmission line configured by the ground lines 16a and 16b and the signal line 14 is not reduced. Therefore, it becomes possible to make the wavelength used in the transmission line shorter and miniaturize the transmission line.